<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>天气案例_监视属性_简写</title>
    <!-- 引入Vue -->
    <script type="text/javascript" src="../js/vue.js"></script>
</head>
<body>
    <!-- 
        
    -->
    <!-- 准备好一个容器 -->
    <div id="root">
        <h1>今天天气很{{ info }}</h1>
        <button @click="changeWeather">切换天气</button>
    </div>
</body>

<script type="text/javascript">
    Vue.config.productionTip = false;   // 阻止vue 在启动时生成生产提示

    const vm = new Vue({
        el: "#root",
        data: {
            isHot: true
        },
        computed: {
            info() {
                return this.isHot ? "炎热" : "凉爽"
            }
        },
        methods: {
            changeWeather() {
                this.isHot = !this.isHot
            }
        },
        watch: {
            // 正常写法
            /*
                isHot: {
                    // immediate: true,    // 初始化时让handler调用一下
                    // deep: true,         // 深度监视
                    handler(newValue, oldValue) {
                        console.log('isHot被修改了', newValue, oldValue);
                    }
                },
            */
            
            // 简写
            /*
                isHot(newValue, oldValue) {
                    console.log('isHot被修改了', newValue, oldValue);
                }
            */
        }
    });

    // 正常写法
    /*
        vm.$watch('isHot', {
            // immediate: true,    // 初始化时让handler调用一下
            // deep: true,         // 深度监视
            handler(newValue, oldValue) {
                console.log('isHot被修改了', newValue, oldValue);
            }
        });
    */ 

    // 简写
    vm.$watch('isHot', function(newValue, oldValue) {
            console.log('isHot被修改了', newValue, oldValue);
        }
    );

</script>
</html>